Health

Estimating prevalence of HIV infection: considerations in the design and analysis of a national seroprevalence survey

Article Abstract:

Currently, estimates of the number of individuals infected with HIV (human immunodeficiency virus) range from 400,000 to 2 million. These estimates have been generated by knowing the prevalence of infection in certain populations at risk and estimating the size of the populations, and by knowing the current incidence of AIDS and the time of latency until the development of AIDS in patients with HIV infection. Knowledge of the prevalence of HIV infection in the United States is necessary so that the course of the epidemic can be anticipated and the needs for clinical resources, public education, and other control measures can be planned. The design and interpretation of a prevalence survey must utilize existing information about the biology and epidemiology of AIDS. If properly designed, such a study can answer questions of policy, such as where the effort is needed for prevention; whether to require testing for HIV infection before individuals are married; whether mass screening of the population is needed; how much money is needed for AIDS treatment; and if a vaccine becomes available, how it should be tested and distributed. The issues to be considered in designing a prevalence survey include cost and accuracy. A stratified sampling strategy, which is the division of the population into homogeneous subpopulations and enrolling participants from these subpopulations, must be used. The size of the sample cluster, or number of people used for the survey from each subpopulation, must be decided to minimize variability while holding down costs. Pretests are helpful to determine how many people who are at risk for HIV infection are willing to be part of a study. Repeated screening of the population is necessary if trends over time, such as the rates of HIV infection by age group, are to be analyzed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Practical issues and considerations in the design of clinical trials for HIV-infected infants and children

Article Abstract:

The number of cases of AIDS in children is small, but is increasing dramatically. In the United States, cases of AIDS in children account for approximately 2 percent of all AIDS cases. Because of the small numbers, clinical trials must be designed carefully so that the questions that are being asked are properly addressed as quickly and efficiently as possible and so that the clinical trials include as many children as possible. There are four categories of children who might be considered for clinical trials: the fetus of an HIV-positive mother; the newborn of an HIV-positive mother; infants over six months old and young children; and adolescents. The results from trials with adults can be extended to children who are in similar stages of disease. However, this approach must take into consideration the similarities and differences between children and adults who have AIDS. Some of the opportunistic infections which develop in adults, including toxoplasmosis and cryptococcal meningitis, are unusual in children. Therefore, these diseases cannot be used as end points in children to assess successful activity of various drugs against the virus. There are certain disease states which occur more commonly in children than adults, including lymphocytic interstitial pneumonia and neurodevelopmental deficits. Certain bacterial infections, especially those with Streptococcus pneumoniae and Hemophilus influenzae, occur more commonly in children than adults. The number of CD4 helper T lymphocytes does not correlate as well with the stage of disease progression in children as it does in adults. It is concluded that new drugs should be tested as early as possible in children. Safety and tolerance studies need to be done in children, but studies which test the effectiveness of the drug can be done in adults. (Consumer Summary produced by Reliance Medical Information, Inc.)

Modeling the relationship between survival and CD4 lymphocytes in patients with AIDS and AIDS-related complex

Article Abstract:

The effect of zidovudine on CD4 T-cells explains only a portion of the improved survival associated with zidovudine therapy. CD4 T-cells, which are a type of white blood cell, are depleted in HIV infection. Previous studies found that increases in CD4 T-cells are associated with prolonged survival. Normally disease progression is used in clinical trials to measure drug effectiveness. In a study of whether CD4 T-cells could be used as markers of treatment response instead, results from two completed studies on the efficacy of zidovudine were analyzed. In both studies, the risk of death increased as CD4 T-cell counts dropped. The risk increased dramatically when the CD4 T-cell count dropped below 50 cells per cubic millimeter. When patients who received zidovudine were compared with those who received placebo, the risk of death was higher for patients who received placebo at all CD4 T-cell counts. This suggests that CD4 T-cells would be of limited use as markers in clinical trials.